Masoneilan 10900 Series Actuators for 500 Series Regulators
Overview
The Masoneilan 10900 is the actuator Baker Hughes designed for its 500 Series pressure regulators. It is offered in two forms: a spring diaphragm actuator for reducing and back pressure regulators, and a differential pressure actuator for the matching differential regulators. The actuator is an air-to-extend stem design, a simple and powerful mechanical device in which the nominal range is the pressure range, in psi, over which the setpoint can be adjusted. Nylon-reinforced neoprene diaphragms give smooth, sensitive operation.
Seven Star LLC is the trusted supplier for Masoneilan in the Sultanate of Oman and supplies the Masoneilan 10900 together with the regulator bodies it is fitted to. Because the actuator is identified by case size and spring range, our Muscat team can read the range on an existing serial plate and confirm a replacement or a different range before an order is placed.
Operating Principle of the Masoneilan 10900
In the spring diaphragm version of the Masoneilan 10900, process pressure acts on one side of a flexible diaphragm and the actuator spring acts on the other. The compression of the spring, adjusted with a spring adjuster, sets the pressure at which the regulator throttles, so a stronger spring means a higher setpoint. The diaphragm conforms to the diaphragm plate, which serves as a flexible upper guide for the actuator stem, and an oil-impregnated bronze bushing in the spring adjuster is the lower guide. The 1/2 in. NPT pressure connection is on the upper diaphragm case.
The differential pressure version senses two pressures. The high-pressure connection, 1/2 in. NPT, is on the upper diaphragm case and the low-pressure connection, also 1/2 in. NPT, is on the diaphragm chamber, so the actuator opens or closes the regulator to hold a set difference between them. Two case families are offered: a low-pressure case rated 60 and 250 psi static, and a high-pressure case rated 600, 1000 and 1500 psi static.
Engineering Design of the Masoneilan 10900
The yoke is ASTM A126 Class B cast iron, the stem is carbon steel with a zinc dichromate plating, and the springs are ASTM A229. Diaphragm cases and spacer rings are ASTM A36 with zinc dichromate coating, and the plunger and stem on differential versions use solution annealed 316 stainless steel where NACE hardness compliance is required. The actuator is shipped with spring compression fully removed to avoid stress on the diaphragm and spring in storage, and it is then adjusted to the specified setting at installation.
Five options extend the standard Masoneilan 10900 construction. OP1 fits a carbon steel yoke usable down to an ambient of -46 degC, OP2 provides NACE compliance with exposed or non-exposed bolting, OP3 adds protection for a corrosive atmosphere, OP4 is an upper cover stockbar and OP5 adds stainless steel bolting, which also applies to coastal and offshore environments. PTFE diaphragm protectors are available where the process fluid is not compatible with the standard diaphragm.
Key Features
The following points explain why the Masoneilan 10900 is specified for 500 Series regulators:
- One actuator family covers reducing, back pressure and differential duty across the 525, 526, 535H, 536H and 535V regulators.
- Spring ranges run from 0.5-3 psi to 400-750 psi, so the same family serves low-pressure gas blanketing and high-pressure process lines.
- Case sizes of 9, 5, 4 and 3.5 in. carry static ratings of 60, 250 and 750 psi, with differential cases rated to 1500 psi.
- Diaphragm choices cover neoprene, silicone and Viton fabrics, from -73 to 204 degC.
- Steam service is supported by mounting the actuator below the body so that a condensate barrier protects the diaphragm.
- Optional carbon steel yoke, NACE construction, corrosive-atmosphere and stainless bolting packages are defined in the tech spec.
- Baker Hughes states that the Masoneilan 10900 has an estimated useful life of 25 years or more with annual inspection and routine maintenance.
- Recommended spare parts, including the diaphragm and O-rings, are identified in the instruction manual.
Industrial Applications
The Masoneilan 10900 goes wherever a 500 Series regulator controls steam, air, gas or liquid pressure: boiler feed and auxiliary steam headers, fuel gas and instrument gas pressure letdown, compressor seal systems and process skids. In Oman these duties appear in power and desalination plants and in the refinery and gas-processing sites around Sohar and Duqm, where a worn or mis-ranged actuator is a common reason for unstable downstream pressure.
In Oman and the GCC, Seven Star LLC supplies the Masoneilan 10900 with the regulators it controls, including the Masoneilan 174 Series self-contained regulator and the 500 Series bodies listed below. We help customers decide whether the Masoneilan 10900 should be the spring diaphragm or the differential version and select a range that keeps the regulator working in the middle of its travel.
Related published Masoneilan pages: Masoneilan 172 Series pressure reducing regulator and Masoneilan Type 87/88 spring-diaphragm actuators.
Technical Specifications
The table lists the published data for the Masoneilan 10900 from the Baker Hughes technical specification, Rev. K, 03/2026.
| Parameter | Specification |
|---|---|
| Model | Masoneilan 10900 Series spring diaphragm and differential pressure actuators |
| Regulators served | Reducing 525, 535H, 535V; back pressure 526, 536H; differential 525-50, 535H-50, 535V-50, 526-50, 536H-50 |
| Action | Air-to-extend stem |
| Spring diaphragm ranges | 0.5-3, 2-10, 6-20, 15-40 (size 9); 30-75 (size 5); 60-125 (size 4); 80-250, 150-300, 150-450, 400-750 psi (size 3.5) |
| Spring diaphragm static limit | 60 psi (size 9), 250 psi (sizes 5, 4, 3.5 low ranges), 750 psi (150-750 psi ranges) |
| Travel | 0.375 in. (9.5 mm) on 500 Series; 0.1 in. (2.5 mm) on 535V; 0.125 in. (3.18 mm) on the 150-750 psi 3.5 in. case |
| Differential pressure ranges | Low pressure: 15-40, 3-12, 10-35, 30-75, 60-125 psi; high pressure: 3-15, 30-85, 5-30, 10-60, 10-30, 75-185, 100-330 psi |
| Differential static limit | 60 and 250 psi (low pressure case); 600, 1000 and 1500 psi (high pressure case) |
| Diaphragm materials | Neoprene with nylon (-32 to 82 degC); silicone with Dacron (-73 to 177 degC); Viton with Dacron (to 204 degC) |
| Connections | 1/2 in. NPT |
| Yoke | ASTM A126 Class B; optional ASTM A352 LCC carbon steel |
| Weight examples | 31 lb (14 kg) for 150-450 psi spring diaphragm; 33 lb (15 kg) for 0.5-3 psi; 68 lb (31 kg) for 100-330 psi high-pressure differential |
Related Masoneilan regulators for the 10900 actuator include the Masoneilan 525 double-seated pressure reducing regulator, Masoneilan 526 back pressure regulator, Masoneilan 535H single-seat pressure reducing regulator and Masoneilan 536H back pressure regulator.
Request a Quote for Masoneilan 10900
To request pricing or technical support for the Masoneilan 10900, send a formal RFQ to the Seven Star LLC instrumentation division with the regulator model, the actuator range and case size from the serial plate, the service fluid and temperature, and whether the unit is a spring diaphragm or differential version. We can confirm the range, advise on availability and lead time and supply the technical specification and manual linked on this page. In Oman and the GCC, Seven Star LLC supplies genuine actuators with manufacturer documentation and local engineering support.
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